Electron discharge device



April 4, 1961 M. l. KAHL ELECTRON DISCHARGE DEVICE Filed Jan. 2, 1959 77ME fsicolvos) INVENTOR Maur/ce 1T Aa/z/ finn im ATTORNEY 2,978,606 ELECTRON DISCHARGE DEVICE Maurice I. Kahl, Seneca Falls, N.Y., assignor, by mesne assignments, to Sylvania Electric Products Inc., Wilmington, Del., a corporation of Delaware Filed Jan. 2, 1959, Ser. No. 784,674 4 Claims. (Cl. 313-470) This invention generally relates to electron discharge devices and more particularly to cathode sub-assemblies adapted for use in cathode ray tubes.

It has been the practice to employ cathodes utilizing heat responsive electron emissive material as the source of beam energy in cathode ray tubes. In such devices, the cathode generally comprises a metallic cylindrical sleeve capped on one end having the emissive coating deposited thereon. A heater or resistance filament is disposed within the cylinder. In order to position the cathode relative to adjacent electrodes, it is normally mounted upon a suitable electrically insulating disc, which is in turn aligned relative to these electrodes. The cathode is disposed in an aperture formed in the. disc and is rigidly mounted therein by means of ferrules, which contact the disc completely around the cathode cylinder.

It has been found that the mass of the disc acts as a heat sink and that the relatively large area in contact with the cathode cylinder and ferrules acts as a highly conductive thermal path which serves to conduct heat away from the cathode and into the heat sink. The

loss of heat at a very rapid rate delays the heating time.

required for the cathode to reach a temperature whereat adequate emission is achieved. This value of emission is one which is capable of providing a visually observable image on the screen of the tube at a given brightness leve The heating time characteristic is becoming ever more important since it is being adopted in the television industry as a figure of merit for the cathode ray or picture tube. Due to the fact that the insulating disc in the previously used cathode disc assembly described above had a large contact area with the cathode and operated as a relatively large heat sink during the very critical initial stages of heating, it was found to be unsatisfactory from the heating time viewpoint.

Accordingly, an object of the invention is to decrease A the aforementioned disadvantages by decreasing the heating time of a cathode ray tube.

A further object is to accelerate emission of the hot cathode employed in a cathode ray tube.

Another object of the invention is to control and inhibit thermal conduction from the cathode while providing a support therefore which is sufiiciently strong to allow mechanical handling and assembly.

The foregoing objects are achieved in one aspect of the invention by the provision of an electrically insulating support for the hot cathode which comprises a disc having a centrally disposed aperture for receiving the cathode defined by a wall formed to provide protrusions for engaging the cathode over a preselected area. This support serves to control the total heat losses from the cathode during initial heating by controlling the thermal conduction therefrom. In effect, the rate of heat loss from the cathode is inhibited and controlled.

For a better understanding of the invention, reference is made to the following description taken in conjunction with the accompanying drawings in which:

Fig. 1 is a sectional view of a heater, cathode, insulating support and grid assembly which is adapted to be employed in a cathode raytube;

Fig. 2 illustrates in perspective the cathode and insulating support assembly shown in Fig. 1;

Fig. 3 is a plan view of the insulating support; and

ice

Fig. 4 illustrates graphically the electrical characteristics of a cathode ray tube utilizing the invention.

The drawings illustrate a sub-assembly 11 of the type adapted for use in a conventional cathode ray or picture tube. This assembly comprises a cathode cylinder 13 and top cap 14 having emissive material 15 deposited thereon. or control grid 17 so that the emissive material 15 is spacedfrom the aperture 19 provided in end wall 21 of the grid. A filament 23 is disposed within cylinder 13 to provide the heat needed to cause electron emission from material 15. During operation of the cathode ray tube, the electrons from material 15 pass through grid aperture 19 and thence to the screen of the tube.

Cathode cylinder 13 is positioned within grid 17 by means of its attachment to support disc 25, which is in' turn mounted intermediate spacer 27 and split sleeve 29. The disc is clamped between spacer 27 on its upper surface and sleeve 29 on its lower surface to provide a rigid mounting therefor. A weld connection is made between sleeve 29 and grid 17 to provide complete assemblage of the components. The sleeve is split into a plurality of segments 31 so that an outward spring pressure is exerted by the segments against the internal wall of the grid to assure optimum fit and alignment.

The cathode cylinder 13 is held upon disc 25 by the upper and lower beads or ferrules 33 which are affixed to the cylinder. However, other means of attachment such as a pressure fit or crimping of the cylinder walls may be used if desired.

The utilizationof spacer 27 and sleeve 29 for the purpose of properly mounting the cathode 13 and disc 25 assembly has been found to be very elfective. However, 7

posed aperture 37. The configuration of the wall pro-l vides a plurality of spaced protrusions 39 interconnected by reentrant portions 41. Radial grooves 43 are formed in disc 25 to increase the surface area or leakage path between cathode cylinder 13 and the metal parts 17 and 27. Since the cathode materials tend to sublime over the surface of disc 25 during operation of the tube, the relatively long and broken electrical leakage path. along with the sharp corners in grooves 43 tend to inhibit formation of an electrically conductive path between the cathode and grid 17. Apertures 45 aid in exhausting the assembly. However, these grooves and apertures need not be employed, thereby providing upper and lower continuous surfaces for the disc.

The protrusions 39, which may but need not have their faces formed in conformance with the periphery of cylinder 13, serve to contact ferrules 33. These ferrules overlie part of protrusions 39 to provide clamping of the disc to the cylinder. When a force fit or crimping between the disc and cylinder is used, the protrusions are in tight frictional engagement with the cylinder. In any event, only a pre-selected surface area of the disc is directly in contact with either the cylinder or the ferrules. As shown clearly in Fig. 2, the reentrant portions 41 are removed from the contact surface.

It has been found that, in most cases, the figure of merit for a cathode ray tube based upon heating time is dependent primarily upon initial heat losses from the cathode rather than on the emission characteristics of material 15. At the very early critical stages of heating;

The cathode is mounted within an electrode these losses are predominantly from thermal conduction into the heat sin formed by the mass of the disc. Therefore, proper selection of the surface area of the disc in contact with ferrules 33 along with the size of reentrant portions 41 provides control of the heat loss from the c linder.

r11 optimum engagement area between disc 25 and cylinder 13 is dependent upon such factors as the type of cathode cylinder material and its size and shape, and the type of material used to form disc 25 as well as the mass and shape of the disc. Therefor, although four protrusions 39 are shown in the drawings, it is to be understood that this number may be varied, as well as the particular configuration of the protrusions in accordance with the required total engagement surface. For example, any number of protrusions could be employed and the engagement surfaces or ends of protrusions 39 could be straight across or formed to a point as well as be ng curved in the manner shown in the drawings or otherwise. In addition, although reentrant portions 41 are illustrated as being circular, it is obvious that many other forms such as ellipses and triangles could be utihzed.

When determining the contact surface area and form of protrusions 39 as well as the dimensions and form of reentrant portions 41 to use with a given cathode-disc assembly, a total engagement surface value should be selected which will be small enough to inhibit initial thermal conduction from the cathode but large enough to prevent an undesirably high thermal radiation within the reentrant portions 41. When the latter occurs, the cathode will tend to operate, after adequate heating, at a temperature which is lower than desired due to higher total heat losses which arises from the higher radiation.

Referring to Fig. 4, curve A illustrates the average heating time of tubes employing prior disc structures which contacted the cylinder 13 or ferrules 33 completely around their periphery. Curve B illustrates this characteristic for tubes using steatite discs 25 for supporting the nickel or nickel alloy cylinders 13. The protrusions 39 engage approximately 60 percent of ferrules 33 when the protrusions and reentrant portions 41 have theform shown in the drawings. The curves show that in 30 seconds, which is near the top limit of the critical period of heating time, curve B is much higher than curve A. In elfect, this points out the fact that the structure described herein on the average produces an in tial emission which is much higher than the average prior device. This increased emission is very often the difierence between an acceptable and an unacceptable tube.

The form of curve B aids in determining the proper total engagement surface of protrusions 39 with ferrules 33. It has been found that the thermal conduction and therefore the total heat losses should be controlled and inhibited at least to some region or point on curve B indicated at X solely for purposes of illustration to provide good heating time characteristics. This point represents approximately the value whereat the thermal conduction is approximately equal to the thermal radiation or until the thermal emissivity of a nickel cathode reaches .15. When using typical triple carbonates of barium, strontium and calcium for emissive material 15, point X may approximate the value of emission whereat the oathode is heated to approximately 700 C.

The invention described herein provides for a cathode ray tube having an improved figure of merit based upon heating time. This improvement is brought about by accelerated initial cathode electron emission, which is in turn caused by inhibition of thermal conduction and therefor total thermal losses from the cathode during the initial stages of heating. In addition, the disc structure still has sufiicient strength to withstand assembly and handling.

Although several embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

1. In an electron discharge device employing a heater positioned Within a hot cathode'h'aving an electron emissive material thereon, a support for rigidly holding the cathode comprisingan electrically insulating disc of substantially uniform thickness having an internal wall defining a centrally disposed aperture, said wall being formed to provide spaced cathode contacting surfaces intereconnected by reentrant portions, said surfaces providing a total cathode contacting surface which controls the thermal conduction losses from said cathode through said surfaces and the thermal radiation losses from said cathode into said reentrant portions to provide substantially steady state cathode emission at a cathode temperature of about 700 degrees C. within approximately thirty seconds after energization of the heater.

2. In an electron discharge device employing a heater positioned within a hot cathode containing nickel and with electron emissive material deposited thereon, a sup port for rigidly holding the cathode comprising an electrically insulating disc'of substantially uniform thickness having an internal wall defining a centrally disposed aperture, said wall being formed to provide spaced cathode contacting surfaces interconnected by reentrant portions, said surfaces providing a total cathode contacting surface which controls the thermal conduction losses from said cathode through said surfaces and the thermal radiation losses from said cathode into said reentrant portions to provide a cathode thermal emissivity of about .15 and substantially steady state cathode emission at about 700 degrees C. within approximately thirty seconds after energization of the heater.

3. In an electron discharge device employing a heater positioned within a hot cathode having an electron emissive material thereon, a support for rigidly holding the cathode comprising an electrically insulating disc of substantially uniform thickness having an internal wall defining a centrally disposed aperture, said wall being formed to provide at least four substantially equally spaced cathode contacting surfaces interconnected by reentrant portions, said surfaces providing a total cathode contacting surface which controls the thermal conduction losses from said cathode through said surfaces and the thermal radiation losses from said cathode into said reentrant portions to provide substantially steady state emission at a cathode temperature of about 700 degrees C. within approximately thirty seconds after energization of the heater.

4. In an electron discharge device employing a heater positioned within a hot cathode having an electron emissive material thereon, a support for rigidly holding the cathode comprising an electrically insulating disc of substantially uniform thickness having an internal wall defining a centrally disposed aperture, said wall being formed to provide atleast four spaced cathode contacting surfaces intereconnected by reentrant portions, said surfaces providing a total cathode contacting surface of about 60 percent which controls the thermal conduction losses from said cathode through said surfaces and the thermal radiation losses from said cathode into said reentrant portions to provide substantially steady state emission at a cathode temperature of about 700 degrees C. within approximately thirty seconds after energization of the heater.

References Cited in the file of this patent UNITED STATES PATENTS 2,641,727 Pohle June 9, 1953 2,717,325 Gosslar Sept. 6, 1955 2,732,512 Briggs Jan. 24, 1956 FOREIGN PATENTS 749,115 Great Britain May 16, 1956 

